Electric fuse



Patented `luly 14, .1925.

ram coulis, or cLmDoN, ENGLAND.

ELECTRIC FUSE.

Application led April 16, 1925. Serial Fo.,28,698.

To all whom 'it 'may concern.'

Be 4it known that I, FRANK CoA'rns, subject of the King of England, residing at Cleadon, in the county of Durham, .Eng- 5 land, have invented certain new anduseful Improvements in Electric Fuses, of which the following is a specification.

This invention relates to electric fuses and has particular reference to fuses for use in 1c high voltage circuits as for example for connecting a power station busbar system to a potential transformer. Such fuses are subjected to heavy currents under short-circuit conditions and in practice diiiiculty is experienced in providing a fuse of such a nature as to clear the short-circuit satisfactorily whilst the destructive eect is limited to the fusible element only.

One known method of dealing With this diiiculty is to employ an external resistance in series with the fuse for the 'purpose of limiting the short-circuit current within the safe rating of the fuse but such a -method entails several disadvantages of which the space occupied by the resistance and its cost maybe mentioned as examples. Obviously the diiiculty and the disadvantages above mentioned are emphasized when the fuses lo are required for use upon extra. high voltage systems.

Many forms of high resistance fuses have been suggested and the fuse wire has been wound 1n spiral grooves in insulating sup- 85 ports or threaded through tubes and in some such constructions the spacearound the Wire has been packed with insulatin and refrac- .tory material such for examp e as asbestos or marble dust. Y

According to the present invention the wire or strip formingthe fuse-is provided with a covering of insulating and refractory material, referably a wound covering of asbestos, w ich restricts the area of the path for the vapour when the fuse is volatilized, and this covered wire is wound in spiral or like form on a support of insulatin malterial or is embedded in such material.

Various constructions may be employed in carr ing out this invention, for instance the en 4 of the spiral or covered wire wound upon the support may be connected to caps or contacts at the ends of the support. A tube 01' cover of some'suitable insulating material may enclose the spiral wire and its support and may fit into the caps. The space between this outer tube and the supported splral may be filled with any desired insulating medium such for example as marble dust or some form of insulating compound. Again the spiral fusible element covered with its layer of refractory insulatmg material and wound on its support may have applied to it and to the support a coatlng of some well-known vitreous enamel which can be baked hard and by its adhesion retains the spiral in position.

In another construction the spiral or like fusible element with its covering may be entirely embedded in an insulating substance which will then act as the support.

In sucha construction the outer cover may be dispensed with.

In the accompan ing drawings,

Figure 1 is an elevation partly in section of one construction of fuse according to this invention, and

Figures 2, 3, 4 and 5 are sections of portions of other constructions of fuses also according to this invention, these fi res being drawn to a larger scale than i re 1.

With reference iirst to Figure 1 t e fuse wire A with a covering of asbestos A1 is wound in the form of a spiral upon a rod or su port B of insulating material supporte cap C. The fuse and its support 1s enclosed in a tube D of insulating material to which the end caps C are cemented or otherwise secured.

Figure 2 may be re arded as an enlarged view of a portlon of igure 1 and the parts bear corresponding reference letters. But Figure 2 also shows the space between the outer tube D and the support B filled with an insulating material such for example as marble dust lor some form of insulating compound. This is indicated at E. A

In the fuse shown in Figure 3 the Wire or strip A with its insulating refracto covering A1 is covered with vltreous or Aike material F such as some Well known vitreous enamel which'can be baked hard and by its adhesion retains the spiral in its posltion on the insulating suplport B. Again a lillmg of insulatn materia E is provlded between the fuse -an its support and the outerinsulating tube D.

in a socket or recess C1 in an end Figure 4 shows the fuse wire A and its insulating and refractory-covering A1 wound in grooves'B1 in the sup ort B.

In the form shown in formed by the wire A and its covering A1 is entirely enclosed by insulating material B2 cast or otherwise formed round it. In this construction there is no need for van i, vouter enclosing tube and the ends of tle llli for said covered conductor which is wound around the support in spiral form, and a c, 1,545,55av

igure i 5 the spiral i coating of vitreous material acting to retain said covered conductor in place on its sup, port. N f

f 2. An electric fuse for high Vvoltage c1rcuits comprising a conductor, a covering of insulating and refractory material aroundsaid conductor acting to restrict the area of c thespath for the vapour when the fuse is volatilized, a support of insulating material for said covered conductor, means attaching Y said covering to said support, a tube of in-` sulating material enclosing said support and covered conductor, conducting caps at the 4 ends of said tube and supporting the ends of said insulating support, and electrical con'- nectionsbetween each end of the covered conductor and the adjacent cap.

ln testimony whereof I have signed my name to this specification.

' FRANK Comms. 

